1. Field of the Invention
The present invention relates to a liquid crystal display used for a display screen of a computer and the like.
2. Description of the Related Art
FIG. 15 is a circuit diagram of a conventional liquid crystal display which includes a control signal generation circuit 1, a grayscale voltage generation circuit 2, source driving circuits 3, gate driving circuits 4, a liquid crystal panel 5 and TFTs 6. The liquid crystal panel 5 has a plurality of source lines 5a and a plurality of gate lines 5b. The control signal generation circuit 1 receives color signal inputs Ri, Gi and Bi, a clock input CLKi and a synchronization signal input Synci and provides color signal outputs Ro, Go and Bo, a clock output CLKo and a synchronization signal output Synco. For example, each of the color signal inputs Ri, Gi and Bi and color signal outputs Ro, Go and Bo is constituted by four bits and is illustrated with an indication xe2x80x9c less than 3;0 greater than xe2x80x9d to represent the four bits. xe2x80x9c less than 3;0 greater than xe2x80x9d represents four bits from a third bit through a 0-th bit. The grayscale voltage generation circuit 2 generates grayscale voltages Vref. The source driving circuits 3 drive the source lines 5a in accordance with the color signal outputs Ro, Go and Bo from the control signal generation circuit 1 and the grayscale voltages Vref from the grayscale voltage generation circuit 2. The gate driving circuits 5 drive the gate lines 5b in accordance with the synchronization signal output Synco from the control signal generation circuit 1. The liquid crystal panel 5 has the multiplicity of TFTs 6 in the form of a matrix which are connected to each of the plurality of gate lines 5b and the plurality of source lines 5a provided in an intersecting relationship with the gate lines 5b. 
FIG. 16 is a characteristic diagram showing the relationship between the grayscale voltages and luminance of the conventional liquid crystal display, and a characteristic A0 represents the relationship between the grayscale voltages Vref from the grayscale voltage generation circuit 2 and the luminance of the liquid crystal panel 5. FIG. 17 is a characteristic diagram showing the relationship between grayscale data and the grayscale voltages of the conventional liquid crystal display, and a characteristic BO represents the relationship between grayscale data represented by the color signal outputs Ro, Bo and Go from the control signal generation circuit 1 and the grayscale voltages Vref. In this example, each of the color signal outputs Ro, Go and Bo is constituted by four bits, and the 4-bit configuration provides 16 types of grayscale data and the grayscale voltage Vref at 16 levels associated therewith. FIG. 18 is a characteristic diagram showing the relationship between the grayscale data and the luminance of the liquid crystal panel of the conventional liquid crystal display, and a characteristic C0 represents such a relationship.
FIG. 19 is a characteristic diagram showing an example of a modification of the relationship between the grayscale data and luminance of the conventional liquid crystal display, in which the characteristic C0 is changed to a characteristic C1 or C2. FIG. 20 is a characteristic diagram-showing the relationship between the grayscale data and grayscale voltages of the conventional liquid crystal display and, for example, it shows the relationship between the grayscale data and grayscale voltage Vref when the characteristic B0 is changed to a characteristic B1.
FIG. 21 shows another example of a conventional liquid crystal display which includes a plurality of grayscale voltage generation circuits 2a, 2b and 2c. 
Referring to FIG. 21, the parts represented by the reference number 1 and the reference numbers 3 through 6 are identical to those in FIG. 15. The grayscale voltage generation circuit 2 includes three grayscale voltage generation circuits 2a, 2b and 2c for changing the relationship between the grayscale voltage and luminance of the liquid crystal display. Reference number 7 represents a selection circuit which selects one of the outputs of the plurality of grayscale voltage generation circuits 2a, 2b and 2c. 
In the conventional liquid crystal display as shown in FIG. 15, in order to achieve multi-level color display, grayscale voltages at predetermined levels are selected from among grayscale voltages at a plurality of levels generated by the grayscale voltage generation circuit 2 based on input digital image data; the grayscale voltages are supplied to the TFTs 6 at the liquid crystal panel 6 through the source driving circuits 3; and an image is displayed by applying the grayscale voltages to the liquid crystal.
For example, in the case of a normally white liquid crystal, an increase in the grayscale voltage applied to the liquid crystal results in a reduction in luminance as indicated by the characteristic A0 in FIG. 16. The grayscale data are digital data, and the grayscale voltages are selected on a digital basis.
FIG. 17 represents the relationship between grayscale data at 16 levels and grayscale voltages as the characteristic B0 in order to provide a simple description of the selection of grayscale voltages on a digital basis. The grayscale voltage generation circuit 2 generates grayscale signals V0 through V15 which are selected based on grayscale data. As a result, the grayscale display characteristic C0 shown in FIG. 18 is provided which is represented by a grayscale data-luminance curve.
FIG. 18 omits representation on a digital basis and schematically shows a grayscale display characteristic relative to input grayscale data.
Most conventional liquid crystal displays have a fixed grayscale display characteristic. However, there is a need for a capability of arbitrarily changing the grayscale display characteristic of a display as shown in FIG. 19 to achieve optimum display in accordance with the preference of the user of the display and the environment in which the display is used.
In the case of a liquid crystal display in which grayscale voltages are selected based on digital data, however, the grayscale voltages must be changed, for example, as shown in FIG. 20, which results in a need for a complicated analog circuit for generating the voltages.
Further, a plurality of grayscale voltage generation circuits 2 may be provided to allow grayscale display characteristics to be changed based on selection at a selection circuit 7, as shown in FIG. 21. However, this also results in a complicated circuit and can increase the cost.
The invention was made in order to solve the abovedescribed problems, and it is an object of the invention to provide a liquid crystal display whose grayscale display characteristic can be arbitrarily changed to achieve optimum display in accordance with the preference of the user and the environment in which the display is used.
A liquid crystal display according to the invention has: a circuit which includes a data conversion circuit for converting digital image input data based on arbitrary algorithm and which outputs digital image output data based on the output of the data conversion circuit; a grayscale voltage generation circuit which outputs grayscale voltages at a plurality of levels; source driving circuits which receive the digital image output data and grayscale voltages and which select and output a grayscale voltage at one level from among the grayscale voltages in accordance with the digital image output data; and a display portion which is configured so as to display an image as a result of the application of the grayscale voltage output by the source driving circuits to a liquid crystal thereof. The data conversion circuit converts the digital image input data so as to change a grayscale display characteristic of the image displayed at the display portion.
There may be provided a plurality,of algorithm defining circuits each of which defines algorithm to be used in the data conversion circuit, and one of the plurality of algorithm defining circuits is selected and used by the data conversion circuit.
A liquid crystal display according to the invention has: a setting portion in which algorithm for converting first digital image data input from the outside into second digital image data is set; a data conversion circuit which uses the algorithm set in the setting portion to convert the first digital image data into the second digital image data; a control signal generation circuit to which the second digital image data converted by the data conversion circuit are input and which outputs the second digital image data and a control signal; a grayscale voltage generation circuit which outputs grayscale voltages at a plurality of levels; source driving circuits to which the second digital image data and control signal output by the control signal generation circuit and the grayscale voltages at a plurality of levels output by the grayscale voltage generation circuit are input, which select a grayscale voltage at one level from among the grayscale voltages at a plurality of levels in accordance with the second digital image data and which output the same in accordance with the control signal; and a display portion which is configured so as to display an image as a result of the application of the grayscale voltage output by the source driving circuits to a liquid crystal thereof. The data conversion circuit converts the first digital image data into the second digital image data so as to change a grayscale display characteristic of the image displayed at the display portion.
A plurality of items of algorithm may be set in the setting portion, and the data conversion circuit may select one of the plurality of items of algorithm to perform data conversion.
Further, the setting portion may be configured so as to allow rewriting of the algorithm from the outside.
Furthermore, the data conversion circuit may convert data in each frame or each group consisting of a plurality of frames.
The digital image data may be constituted by red, green and blue color signals, and the data conversion circuit may perform data conversion on each of the red, green and blue color signals.
In addition, the data conversion circuit may be incorporated in an integrated circuit that constitutes the control signal generation circuit.